The show is pretty not nuanced at all about how it presents the act of sex. The psychological dynamics are probably what fly by pretty easily if you're a child. (Akio and Touga especially.) I wonder about the cultural/moral ones--do these kids know it's all fucked that Akio sleeps with his sister? Or do they sympathize with Nanami's hero worship of her brother? Because the latter relationship especially does seem like a trope--anime doesn't really back down from the whole maybesortoffeelslikeincest thing. Is it supposed to squick kids out, or be a release fantasy for their weird desire to bang their older siblings?

I wonder about the cultural/moral ones--do these kids know it's all fucked that Akio sleeps with his sister? Or do they sympathize with Nanami's hero worship of her brother? Because the latter relationship especially does seem like a trope--anime doesn't really back down from the whole maybesortoffeelslikeincest thing. Is it supposed to squick kids out, or be a release fantasy for their weird desire to bang their older siblings?

The trope is (socially) Forbidden Love , which is rampant in Josei and the sophisticated end of Shoujo anime/manga.  The FB Trope commonly includes LGBT + Incest elements, and is used to put (both good and evil) characters in angsty, emotional situations that tug at the viewers' heartstrings.

And yes, kids totally knows it is wrong for Akio and Anthy to sleep with each other - especially in the mutually manipulative way that it happens.  It is there to disillusion viewers - who might otherwise think Akio is classy and Anthy pure - and force them to see these two as 'corrupted/perverted' 'adults' (despite their being 19 and 14 physically).  These characters are both 'against social norms'/ 'deviant', and thus 'dangerous'/'prone to be evil' as per shoujo tropes.

PS: Anthy is not presented as a 'child' despite her 14 yr old guise, thus why the character's mature voice and tone.  I would go further by elaborating on how her her turn as the openly malevolent 'Mamiya' is there to disqualify her as a 'damsel' and make plain her status as a 'villain', but that would be too derailing for this thread.

Ah, well, I showed my sister (Toe) the show and the movie when she was 9... It was awesome, we watched it like two or three times together and always talked about it. Then again, I was also reluctant to show it to her friend of the same age because I didn't think it'd be right for her. My other sisters, who were 11 and 14 at the time, also watched it, and I was 17. So...yeah...I have no idea. I guess it just depends. And I still don't know how "deeply" any one of us understood it, but I spent a lot of time reading about it here while I watched it (7/8 times)